1. Field of the Invention
The present invention relates generally to methods of securing acetabular implants, and more particularly to an apparatus and method of securing acetabular augments alone, or in combination with an acetabular shell, to a hip using the canal of the ilium.
2. Related Art
In the past, the iliac canal has been utilized for fixedly securing an artificial acetabular bearing surface to pelvic bone. FIG. 1 illustrates one example of such a prior art device. Shown in FIG. 1, is an all-metal Ring prosthesis device (900) which is configured for mounting within the iliac canal. Device (900) typically comprises a shank (901) having threads (902) thereon, a shaft base (903), a transition area (904), and a bearing cup (905) having an inner bearing surface (907) and a rim (906). Typically, device (900) is constructed as one, homogeneous, monolithic, metal piece, which leaves no adjustability or material options to a surgeon. Moreover, once the shank (901) of the device (900) is secured into the iliac canal, the orientations of the bearing cup (905), the rim (906), and the bearing surface (907) relative to the ilium or acetabulum is fixed concentrically with the shank (901). Therefore, fixation of the device (900) may come at the expense of not providing the optimum head coverage necessary for stability throughout a range of motion.
FIGS. 2a-2d illustrate the method steps of installing said Ring prosthesis device (900). First, a canal guide (922) that is mounted on a base (920) is inserted into the acetabulum. The canal guide (922) is inserted into the intramedullary canal of the ilium (i.e., the “iliac canal”) and is then left inside the iliac canal. Second, a cannulated reamer (924) slides over the canal guide (922) and reams out the iliac canal. The canal guide (922) and reamer (924) are then removed from the iliac canal. Thirdly, a frustoconical reamer (926) having a cutting edge (928) bores out a frustoconical countersunk recess in the acetabulum. The countersunk recess provides a clearance for the transition area (904) and the bearing cup (905). Lastly, the Ring prosthesis device (900) is inserted into and secured within the iliac canal by screwing the device (900) into the iliac canal. Torque engagement means (930) is provided on or adjacent to the exposed rim (906).
FIGS. 3a and 3b illustrate another example of a prior art Ring prosthesis (950) called an uncemented polyethylene-on-metal (UPM) hip prosthesis. The UPM hip prosthesis (950) is a successor to the all-metal Ring prosthesis (900) shown in FIG. 1, and similarly utilizes the iliac canal for fixedly securing an acetabular bearing surface to pelvic bone. The prosthesis (950) includes a frustoconical portion (954) which connects a bearing cup (956). The bearing cup (956) has a generally hemi-spherical bearing surface (955), and the frustoconical portion (954) has an eccentric or offset shaft (952) having protuberances thereon. A metallic ring (953) is centered within a groove (957) to allow the rim of the bearing cup (956) to be visible on radiographs.
Prostheses (950) such as the one shown in FIGS. 3a and 3b are typically formed from a monolithic block of ultra-high-molecular-weight polyethylene and may generally be described as an offset conical cup having a finned intraosseous peg mounted thereon. Since the UPM prosthesis (950) is eccentric, it relies on a wedge press-fit into an accurately reamed acetabulum, rather than concentric screwing into the iliac canal.
The eccentric frustoconical portion (954) serves to prevent rotation and to allow small amounts of version adjustment for better head coverage and stability. Grooves extending along the longitudinal axis of the frustoconical portion (954) give additional rotational stability. The prosthesis (950) is fitted into a reamed track created through the centre of the iliopubic buttress and the cup is punched into position. Acetabular prostheses (950) shown in FIGS. 3a and 3b are generally used in combination with either a Ring or a Norwich-type of uncemented femoral component.
FIG. 26 illustrates some examples of prior art Trabecular Metal™ acetabular augments (1000, 1002, 1004, 1006) provided by Zimmer, Inc. The augments are composed of porous tantalum and are intended to fill large bone voids during revision hip arthroplasty surgery, so that acetabular cup stability can be achieved (acetabular cup not shown). These prior art augments do not have protrusion portions configured for insertion into the IM canal of the ilium. The augments also lack a means for mounting the augment to the IM canal of the ilium. Even if a screw (not shown) was to be inserted through one of the holes (1020) provided on some of the augments (1000, 1002, 1004) and into the IM canal of the ilium according to the teachings presented herein, the augments would not seat correctly within the acetabulum, would become unstable, and would not function as intended. Lastly, these prior art augments (1000, 1002, 1004, 1006) are not designed or intended to be modular, interchangeable, interconnectable, and adjustable as are the augments of the present invention.
To this end, all current acetabular prostheses utilizing the iliac canal for fixation do not provide a surgeon with modularity, intraoperative options, and/or material choices. Additionally, all conventional augments designed to fill large bone voids do not provide a surgeon with the option to use the iliac canal as a means for providing prosthesis support and indicating proper orientation in severe cases.
Moreover, the prior art acetabular prostheses (900, 950) described above have been designed for and used only for primary hip surgeries (i.e., first hip surgery). That is, such prior art devices utilizing the iliac canal for fixation are not intended to address the many special circumstances, substantial bone losses, poor bone quality, and other challenges that face a surgeon during complex revision hip surgeries (i.e., surgeries after a first hip surgery).